Amsterdam is playing host to an extraordinary reunion this autumn—not of long-lost relatives, but of paintings, people, and even a humble chair that once sat at the heart of Vincent van Gogh’s most human and heartfelt works. In a quietly moving exhibition titled “Van Gogh and the Roulins: Together Again at Last,” the Van Gogh Museum has gathered the scattered portraits of Joseph Roulin, the bearded postal clerk of Arles, along with his wife Augustine, their sons Armand and Camille, and baby daughter Marcelle—subjects who offered the lonely Dutch artist far more than just their likenesses. They gave him friendship, stability, and a sense of belonging during one of his most turbulent yet creatively explosive periods. From July 1888 to...